1. Field of the Invention
The present invention relates to a vehicle steering device of a by-wire method, and more particularly, to means that makes smooth the control of driving for an operation-side motor, which supplies an operating reaction force to a rotation operating member.
2. Description of the Related Art
In the related art, a vehicle steering device of a mechanical method in which a steering shaft is connected with a steering member via a mechanical power transmission mechanism, has been used as a vehicle steering device. However, in recent years, a vehicle steering device of the by-wire method is proposed, which converts the rotation state of a steering shaft into electric signals, and controls the driving of a steering-side motor provided at a steering member based on the electric signals, and controls the driving of an operation-side motor that supplies an operating reaction force to a rotation operating member of the steering shaft, and supplies a desired operating reaction force to the rotation operating member.
FIG. 6 is a structure view showing an example of a vehicle steering device of the by-wire method, which has been conventionally proposed. The vehicle steering device includes a steering shaft 1; a rotation operating member 2 such as a steering wheel that is operated to rotate the steering shaft 1; an absolute operation angle detecting means 3, whose rotating portion is attached to the steering shaft 1, and which detects the absolute operation angle of the rotation operating member 2; an operation-side motor 4 that supplies an operating reaction force to the rotation operating member 2 via the steering shaft 1; a speed reduction mechanism 5 which is interposed between the steering shaft 1 and the operation-side motor 4 to reduce the operating reaction force generated at the operation-side motor 4 and to transmit it to the steering shaft 1; a steering shaft 7 provided at a transmission mechanism 6, a steering-side motor 8 that rotates the steering shaft 7; a steering angle detecting means 9 that detects a steering angle, and a control means 10 that generates driving signals M1 for the operation-side motor 4 and driving signals M2 for the steering-side motor 8 based on absolute operation angle signals θ1 outputted from the absolute operation angle detecting means 3 and steering angle signals θ2 outputted from the steering angle detecting means 9. Meanwhile, the transmission mechanism 6 is constituted with a pinion gear 11 fixed to the steering shaft 7, a rack shaft 12 having a rack gear engaging with the pinion gear 11, and a link mechanism 14 having an axle 13 driven by the rack gear 12 (for example, see Japanese Patent Unexamined Application Publication No. 2003-252223).
The control means 10 generates and outputs driving signals M1 for the operation-side motor 4 based on the absolute operation angle signals θ1 and the steering angle signals θ2. Therefore, like the vehicle steering device of the mechanical method, the rotation operating member 2 can be supplied with operating reaction force according to the operating angle and direction of the rotation operating member 2. Also, the control means 10 generates driving signals M2 for the steering-side motor 8 based on the absolute operation angle signals θ1 and the steering angle signals θ2, and outputs them. Therefore, like the vehicle steering member of the mechanical method, the steering member 6 can be steered in accordance with the operating angle and direction of the rotation operating member 2, and road state, etc.
However, in order to supply the rotation operating member 2 with smooth and continuous operating reaction force, that is, a force that does not cause a driver to feel uncomfortable in controlling the driving of the operation-side motor 4, it is required to control the driving smoothly or with high resolution. Also, in order to control the driving smoothly or with high resolution, a detecting means having high resolution is required.
However, the detecting means having high resolution enough to perform smooth driving control usually has a high price or a low durability, therefore, it is difficult to control the driving of the operation-side motor smoothly.